The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in the present disclosure and are not admitted to be prior art by inclusion in this section.
The 3GPP Long Term Evolution (“LTE”) Release 10 (March 2011) (the “LTE Standard”) provides for an evolved packet system (“EPS”). An EPS may include an evolved universal terrestrial radio access network (“E-UTRAN”) and an evolved packet core (“EPC”).
LTE Releases 10 and later are known as LTE Advanced (“LTE-A”). LTE-A provides for the deployment of a relay node (“RN”) in an E-UTRAN. The RN may be between user equipment (“UE”) and an evolved NodeB (“eNB”) serving the RN, called the “donor” eNB, or “DeNB.” The DeNB may in turn be in communication with components of an EPC, such as a mobile management entity (“MME”) and/or a gateway (such as a serving gateway, or “SGW”).
Various nodes of an EPS may communicate using various logical interfaces. For example, an eNB may communicate with an MME/SGW over an S1 interface. An eNB may communicate with a DeNB over an X2 interface. An RN may communicate wirelessly with a DeNB using a modified version of the E-UTRAN radio interface, called the “Un” interface.
A downlink signal may include a UE specific reference signal (“USRS”), which may be used by a UE device to demodulate downlink user and/or control data, and/or a common reference signal (“CRS”) used to determine things like channel quality. Sometimes a downlink USRS is referred to as a “downlink demodulation reference signal (“DMRS”), particularly in Release 10 of LTE and beyond.
When an RN communicates with a DeNB over the Un interface, a relay physical downlink control channel (“R-PDCCH”) may be multiplexed with a relay physical downlink shared channel (“R-PDSCH”) in a physical resource block (“PRB”) pair. However, in a non-interleaved R-PDCCH (e.g., mode 2), the Un interface's physical downlink shared channel (“PDSCH”) transmission mode may be based on a USRS, rather than a CRS. In such cases, there may be either two {7, 8} or four {7, 8, 9, 10} logical antenna ports reserved, or “unused,” for the USRS.
To determine whether two or four antenna ports are reserved for the USRS, it has been proposed that a bit may be added to a higher layer. This technique may save as many as six resource elements (“RE”) per slot, and may reduce blind decoding complexity. However, it may require modification of the LTE Standard and may add a higher signaling transmission delay.
Alternatively, it has been proposed that, in a non-interleaved R-PDCCH, the maximum number of USRS ports (four) may be assumed to be used in the R-PDCCH. This technique may avoid the added overhead associated with higher-layer signaling, but may waste REs where only two antenna ports are unused. This technique also may increase blind decoding complexity because there may be a need for more rank format detection. Moreover, it may add a blind decoding delay for rank.